website: add /cloud design partners page and shared shell

- New /cloud page with signup form (email, name, company, role, message)
  posting to a Discord webhook via a TanStack Start server function on
  the Cloudflare Worker. Webhook URL read from DISCORD_WEBHOOK_URL secret.
- Extract SiteShell, SiteFooter, FAQItem from landing-page.
- Migrate /privacy, /download, /blog, /changelog, /cloud to SiteShell so
  they share header + footer with consistent width.
- Add /cloud to header and footer nav.
- Make /docs sidebar full-width; bump footer text from xs to sm.
- Add Cloudflare Workers types and ignore .dev.vars.

packages/website/src/routes/docs.tsx

@@ -39,14 +39,14 @@ function DocsLayout() {
         </nav>
       </header>
 
-      <div className="max-w-5xl mx-auto flex">
+      <div className="flex">
         {/* Desktop sidebar */}
         <aside className="hidden md:block w-56 shrink-0 border-r border-border p-6 sticky top-0 h-screen">
           <Link to="/" className="flex items-center gap-3 mb-8">
             <img src="/logo.svg" alt="Paseo" className="w-6 h-6" />
             <span className="text-lg font-medium">Paseo</span>
           </Link>
-          <nav className="space-y-1">
+          <nav className="space-y-1 -ml-3">
             {navigation.map((item) => (
               <Link
                 key={item.href}